Chroma-keying and virtual set technology enable the actor in the studio to appear as if he is in a more complex environment. Using this technology, scenes comprised of a number of sources, such as live video and computer graphics can be created and combined together.
In many television programs which are broadcast from television studios, live video is combined with backgrounds which were prepared in advance. This technology is called "chroma-key". The backgrounds used in this technology can be still photographs, videotape or any other picture.
The actor (the newscaster, weather forecaster, etc.) stands in front of a plain blue screen in the studio. The television camera shoots both the actor (live video) and the blue screen. The resulting picture is then transferred to a chroma-keyer, for processing. At the same time, a background picture from a different source (such as another camera, pre-taped video or computer graphics) is transferred to the chroma-keyer.
Both pictures, the live and the background picture, are combined in the chroma-keyer and broadcast as one picture which shows the live video on the background. For example, the final result can be a weather-forecaster standing in front of a weather map which cannot be seen at all in the physical studio.
The chroma-keyer can differentiate between the live video and the blue background, according to the pixels. Wherever a pixel from the live video is identified, it is transferred to the combined broadcast picture. Wherever a pixel from the blue screen is identified, the appropriate pixel from the background is placed into the broadcast picture. In this way, a new picture is created and broadcast, using the background which was chosen.
In the above technology, the actor finds himself in a virtual space, which he does not actually see during shooting of the scene. The actor must therefore imagine the set and practice long hours in order to point in the right direction or avoid walking into virtual walls, people and other objects which are part of the set.
There are two ways currently used to help the actor find his way around within the set. Because neither of the solutions is perfect, the two are usually combined together:
1. Marking the places of objects and of the actor himself on the floor with masking tape. This solution is problematic in scenes which are comprised of a number of sets and for scenes in which the integrated object is in movement. PA1 2. A monitor which displays the integrated picture for the actor. This solution causes the actor to focus his gaze on places which are not necessarily part of the scene. For example, the weather forecaster may need to point to a map on the wall in back of him, but in order to see the feedback on the monitor regarding the location of his finger, he is required to look straight ahead. PA1 1. A flash of light which is synchronized with the cameras. PA1 2. Sounds to signify events.
There are also a number of techniques which enable the actor to find his place so that he can react in time to various events: